Before we get too far down the road, if your engine has a harmonic balancer like this, and a flexplate like this, it could be a heavy rod forged steel crank engine. This era was a real mish-mash with Mopar.

3512017 Harmonic Damper.jpg1970 10238 Forged Crank Flexplate - 1.JPG

"We live in a time when intelligent people are being silenced so that stupid people won't be offended".